Generally, a blender blade has two blade wings extending in opposite directions from a blade body. Each of the two blade wings are equipped with cutting surfaces along their leading edges. During operation of a blender, the blender blade rotates about an axis of rotation, and the cutting surfaces cut through the working medium provided in the blender pitcher. Oftentimes, the blade wings are angled in relation to the blade body to provide the blade wings with angles of attack. Varying the angles of attack of the blade wings is used to control the axial flow of the working medium.
In order to understand the consequences of angling the blade wings in relation to the blade body, the angle of attack in relation to airfoils must be understood. With airfoils, the angle of attack is determined in relation to the chord line of the airfoil. The chord line is the line drawn from the leading edge to the trailing edge of the airfoil, and the angle of attack is the angle formed between the chord line and horizontal. As the angle of attack of the airfoil is varied, the “lift” generated by the airfoil is also varied.
For example, when an airfoil has a positive angle of attack, the flowing medium impinges on the lower surface of the airfoil. Consequently, the angle of attack causes the lower surface to deflect flowing medium away from the airfoil. The amount of deflection is related to the orientation of the airfoil. That is, there is more deflection when there is a high angle of attack and less deflection when there is a low angle of attack. Such deflection generates low pressures adjacent the upper surface of the airfoil. For example, the lower surface pushes flowing medium away from the path of the airfoil, and an absence of flowing medium is thereby created adjacent to the upper surface of the airfoil. Due to this absence of flowing medium, low pressures are provided adjacent the upper surface, and these low pressure generate the above-discussed lift. As such, higher angles of attack produce lower pressures adjacent the upper surface to generate more lift, and lower angles of attack produce lower pressures adjacent the upper surface to generate less lift.
The lift generated by the angle of attack of the above-discussed airfoil can be equated with the axial flow generated by the angle of attack of a blade wing. However, unlike the above discussed airfoil, the angle of attack of a blade wing is determined by the forward or rearward “twist” of the blade wing (relative to its leading edge) along its longitudinal length. This twist determines how much working medium impinges the upper surface or lower surface of the blade wing. Without such impingement of working medium, the angle of attack would effectively be zero. For example, if the blade wing was angled upwardly or downwardly (but not twisted forwardly or rearwardly), the working medium would not impinge the blade wing, and the angle of attack of such a blade wing would be effectively zero.
To create the necessary angle of attack, the blade wing is twisted forwardly or rearwardly. When the blade wing is twisted forwardly, the working medium impinges the upper surface, and when the blade wing is twisted rearwardly, the working medium impinges the lower surface. The amount of twisting determines the amount of impingement, and amount of axial flow, while the direction of the twisting (forwardly or rearwardly relative to its leading edge) determines the direction of the axial flow. For example, if the blade wing is twisted forwardly relative to its leading edge, the working medium will impinge the upper surface of the blade wing, and low pressures will be generated adjacent the lower surface, thereby drawing working medium from above to below the blender blade. On the other hand, if the blade wing is twisted rearwardly relative to its leading edge, the working medium will impinge the lower surface, and low pressure will be generated adjacent the upper surface, thereby drawing working medium from below to above the blender blade. Either way, working medium is drawn through the cutting pattern of the blade wing.
Because the blade wings must be twisted to generate the necessary flow of working medium, the cutting pattern defined by the orientation of the leading edges of the blade wings is substantially frusto-conical. In fact, any twisting of the blade wing to adjust the angle of attachment will create a substantially frusto-conical cutting pattern. However, ideal cutting patterns have substantially planar components. Therefore, there is a need to control the axial flow of the working medium (both the amount and direction thereof) irrespective of the angle of attack of the blade wing. Such independent control would allow the cutting pattern to have a substantially planar component to create an efficient impact vector, and avoid the necessity of providing both blade wings with an angle of attack.